2011 Annual Report of the Commission on Magnetic Structures

The Commission on Magnetic Structures (CMS) of the IUCr was established ad interim by the Executive Committee in January 2011, and confirmed by the General Assembly on Wednesday, 24 August 2011 at the XXII IUCr Congress in Madrid Spain, with Laurent Chapon (UK) as Chair, Branton Campbell (USA) as Secretary, and the following as members: Jane Brown (France), Daniel Litvin (USA), Vaclav Petricek (Czech Republic), Alexander Pirogov (Russia), Vladimir Pomjakushin (Switzerland), Juan Rodriguez-Carvajal (France), Taku Sato (Japan) and Wieslawa Sikora (Poland). Manuel Perez-Mato (Spain) of the IUCr Executive Committee and Teresa Fernandez-Diaz (Institut Laue Langevin, France) of the Commission on Neutron Scattering were appointed as consultants to the commission. Of the 12 members and consultants to the commission, 8 attended the first formal commission meeting in Madrid on Friday, 26 August 2011.

The original terms of reference presented with the request to create the commission are as follows:

Establish standards for the description and dissemination of magnetic structures and their underlying symmetries (representations of propagation vector group, ‘complete’ representation of the group necessary for multi-k structures, 3D magnetic Shubnikov space groups, superspace symmetry … ), and promote these standards within the IUCr and among other research communities that rely on magnetic structure information.

Develop CIF standards for magnetic structures and promote their use in crystallographic software. This activity will be developed in collaboration with the IUCr Committee for the Maintenance of the CIF Standard (COMCIFS).

Develop a database for magnetic structures based on the sharing of magnetic CIF files.

Cooperate with other IUCr Commissions in establishing and maintaining standards of common interest, such as magnetic symmetry-group tables, magnetic nomenclature and magnetic form factor data.

Encourage communication and cultivate consensus among research communities that have independently developed diverse approaches to characterizing and describing magnetic structures.

Promote the sponsorship and organization of magnetic-structure sessions, symposia, workshops and schools at triennial congresses of the IUCr, at the meetings of its Regional Associates, and at the meetings of other professional societies that tend to rely heavily on magnetic structure information. This should include sessions dedicated to the analysis of neutron scattering data and magnetic X-ray scattering data.

The commission will initially work to define a minimal description of a magnetic structure that encompasses two broadly divergent ways of thinking: the “crystallographic” approach that employs magnetic Shubnikov symmetry groups, and the “propagation vector” approach that treats amplitudes and phases of Fourier components of the magnetic structure. Furthermore, with both of these approaches, one can either parameterize a magnetic structure in terms of traditional atomic coordinates or in terms of irrep basis functions from group representation theory. Because each of these approaches and parameterizations have special areas of application and strong historical precedents, it would be highly desirable to demonstrate how their minimal descriptions can be conveniently interconverted. Beyond this initial focus, the commission also looked to the future by establishing subcommittees to study the issue of a new volume of the International Tables on magnetic space groups, the creation of a magnetic CIF dictionary, and the development of a magnetic structure database.

Commission members presented workshop components at a variety of meetings in 2011 on magnetic symmetry, magnetic space-groups, the symmetry-mode analysis of magnetic structures, and the Rietveld refinement of magnetic structures against neutron diffraction data. These were not specifically organized under the auspices of the ad interim commission, but substantially furthered its objectives. Concrete plans for future meetings are also included.